In a public or private ISDN network where features such as call transfer and call redirection ("call forwarding") may occur, highly inefficient connections may result. For example, suppose a person in San Francisco calls a person in New York who subsequently transfers the call to a person in Los Angeles. The resulting connection will traverse the continent twice and be more than 6,000 miles long, even though the parties actually in the call are only a few hundred miles apart. In such an environment, it may be advantageous for the network to automatically improve (e.g., shorten) the connection between the parties by selecting a new path through the network and by switching to the new path through the network even as the parties continue talking.
This process is known as path replacement. The protocol and procedure for path replacement have been standardized by ISDN standards bodies. However, in current networks, when a path is replaced, e.g., because of a redirection of a call such as a transfer, there is no guarantee that the replacement path is better than the original one. The path may in fact be worse (e.g., more costly).
What is needed is an ISDN path replacement procedure that is driven by comparisons of path quality.